Several processes are known for the conversion of ethylene, higher olefins, and combinations of olefins to the corresponding alcohol by a hydration reaction. Typically, the hydration reaction produces a product mixture comprising an alcohol and an ether, each having the same carbon chain length as the olefin, in equilibrium with the olefin and water or steam. The thermodynamics and hence the equilibrium of the hydration reaction is such that formation of the alcohol and ether product mixtures is more favourable at low temperatures and high pressures. The attainment of the equilibrium is promoted through the use of a hydration catalyst. Capital and operating costs are lower when the hydration reaction is performed under mild conditions, however the equilibrium amount of the alcohol in the reaction mixture at low temperature and pressure is lower than the equilibrium amount of alcohol in the reaction mixture at low temperature and high pressure.
Examples of such prior art processes include Rolf-Rainer et al. in U.S. Pat. No. 4,760,203, issued in 1988, which describes the production of isopropanol, also known as IPA or 2-propanol or isopropyl alcohol, by hydration of a propene-containing hydrocarbon stream using an acidic cation exchange resin catalyst and a series of interconnected reactors in series. In each of the reactors an aqueous stream and a parallel hydrocarbon stream flow in opposite directions, thereby effecting separation of a product isopropanol rich stream from the reaction mixture. Dettmar et al. in U.S. Pat. No. 4,760,202, issued in 1988, describe the hydration of isoolefins having 4 or 5 carbon atoms to produce tertiary alcohols using a counterflow process and a hydration catalyst. Ramachandran and Dao in U.S. Pat. No. 5,488,185, issued in 1996, describe the hydration of an olefin in a mixture with an alkane to the corresponding alcohol in the presence of a hydration catalyst. Schmidt in U.S. Pat. No. 4,469,903, issued in 1984, describes a process for the production of an aliphatic alcohol, and in particular isopropanol, by the direct hydration of an olefinic hydrocarbon. The product alcohol in the equilibrium mixture is recovered from a water-rich hydration zone effluent stream by countercurrent liquid-liquid extraction against a paraffinic solvent.
Smith, Jr. in U.S. Pat. No. 5,221,441, issued in 1993, describes a method for operating a distillation process for three particular chemical production processes. One of said processes is the production of tertiary butanol, also known as tertiary butyl alcohol, by the hydration of isobutene, also known as 2-methylpropene or isobutylene, using an acid cation exchange resin. The acid cation exchange resin must be maintained in a wetted state by contact with water present in a liquid phase to maintain catalytic selectivity. When the acid cation exchange catalyst is not in contact with the liquid phase the catalyst loses selectivity to tertiary butanol due to loss of water.
In each of the above processes the catalyst is characteristically a hydrophilic acidic hydration catalyst. Further, in each of the above processes the product is wet, and at least one additional refining step is required for recovery of anhydrous liquid product.
Recovery of an alcohol in a substantially anhydrous state from an azeotropic mixture with water is an expensive and complex component of many industrial processes for the production of the alcohol.
As described above, several processes are known for the conversion of an olefin to the corresponding alcohol by a hydration reaction. Typically, the hydration reaction produces an alcohol, or a product mixture comprising a mixture of said alcohol and an ether, the alcohol and the ether each having the same carbon chain length as the olefin, in equilibrium with the olefin and water. The thermodynamics and hence the equilibrium of the hydration reaction is such that formation of the alcohol is more favorable at low temperatures and high pressures. The attainment of the equilibrium is promoted through use of a hydration catalyst. Although capital and operating costs are lower when the hydration reaction is performed under mild conditions, the equilibrium amount of the alcohol in the reaction mixture at low pressures is lower than the equilibrium amount of alcohol in the reaction mixture at high pressures. Several catalysts having acidic properties are useful for the hydration of an olefin to the corresponding alcohol. Said catalysts include acidic cation exchanged resins, inorganic acids and acids supported on inorganic supports. All such prior art catalysts are hydrophilic.
Alcohols are often sold in different grades, depending on the level of water they contain. For example, industrial ethanol has approximately 96.5% (vol) ethanol, the balance being water and a small amount of crude pyridine to “denature” the material, and sometimes a colouring agent. Denatured spirit has 88% (vol) ethanol, water and denaturing compounds. Fine alcohol (96.0–96.5% vol ethanol) is not denatured because it is used in preparation of pharmaceuticals, cosmetics and products for human consumption. Absolute alcohol must have at least 99.7–99.8% vol ethanol, and is used in the preparation of pharmaceuticals and products for human consumption. Normally, absolute alcohol is sold with over 99.9% vol ethanol. Conventional processes for production of ethanol, isopropanol and other alcohols by hydration of an olefin produce a product mixture containing both said alcohol and water. Therefore several methods have been developed by which fine or absolute grades of the alcohol can be recovered from the product mixture. Each such method is costly, with the consequence that fine and absolute grades of alcohol are significantly more expensive to produce than grades containing higher amounts of water.
One prior art approach is to separate a product mixture containing an alcohol and water using a third liquid that selectively removes the alcohol from the product mixture by absorption of the alcohol in the third liquid. Examples of such processes for recovery of light alcohols are described by Rolf-Rainer et al. in U.S. Pat. No. 4,760,203, issued in 1988, by Dettmar et al. in U.S. Pat. No. 4,760,202, issued in 1988, and by Schmidt in U.S. Pat. No. 4,469,903, issued in 1984.
Another prior art approach is first to distill the alcohol from the product mixture as an azeotropic mixture containing said alcohol and water. The water is then removed from the azeotropic mixture by use of a third fluid that also forms an azeotropic mixture with water. The volatile third component is added to the azeotropic mixture of alcohol and water. The mixture is then separated by distillation, the third component forming an azeotropic mixture with water that has a boiling point lower than a boiling point of the azeotropic mixture of the alcohol and water. The third component and the water are thereby distilled from the mixture to leave the alcohol as a liquid product having a water content lower than a water content of the original azeotropic mixture. Separation of azeotropic mixtures is described, for example, by Hoffman in Azeotropic and Extractive Distillation, Interscience Library of Chemical Engineering and Processing, John Wiley and Sons, New York (1964), pages 165–168 and 179–203 and by Wankat in Equilibrium Staged Separations, Elsevier, New York (1988).
Normally, hydration under mild conditions of an olefin having a carbon chain length of at least 4 carbon atoms produces the corresponding alcohol, but only negligible or undetectably small amounts of the corresponding ether. Linnekoski et al. in Applied Catalysis A: General, vol. 170 (1998), pages 117–126, measured and compared the activation energies for hydration of isoamylenes (2-methyl-1-butene and 2-methyl-2-butene) to form 2-methyl-2-butanol (t-amyl alcohol) and etherification of the same isoamylenes with ethanol to form ethyl (2-methyl-2-butyl) ether (ethyl t-amyl ether). The activation energy for the etherification reaction was 117.7 kJ.mol-1, which value is considerably greater than the activation energy for the hydration reaction of the same olefins to 2-methyl-2-butanol, 79.9 kJ.mol-1. Thus it is to be expected that there will be negligibly small conversion of 2-methyl-2-butenes to di-(2-methyl-2-butyl) ether (di-t-amyl ether) during hydration of 2-methyl-2-butenes to 2-methyl-2-butanol under mild conditions